End of the Kiaman Superchron in the Permian of SW England: magnetostratigraphy of the Aylesbeare Mudstone and Exeter groups

The chronology of Permian strata in SW England is fragmentary and largely based on radiometric dating of associated volcanic units. Magnetostratigraphy from the c. 2 km of sediments in the Exeter and Aylesbeare Mudstone groups was undertaken to define a detailed chronology, using the end of the Kiaman Superchron and the overlying reverse and normal polarity in the Middle and Upper Permian as age constraints. The palaeomagnetic directions are consistent with other European Permian palaeopoles, with data passing fold and reversal tests. The end of the Kiaman Superchron (in the Wordian) occurs in the uppermost part of the Exeter Group. The overlying Aylesbeare Mudstone Group is early Capitanian to latest Wuchiapingian in age. The Changhsingian and most of the Lower Triassic sequence is absent. Magnetostratigraphic comparison with the Southern Permian Basin shows that the Exeter and Aylesbeare Mudstone groups are closely comparable in age with the Havel and Elbe Subgroups of the Rotliegend II succession. The Altmark unconformities in these successions appear similar in age to the sequence boundaries in SW England, indicating that both may be climate controlled. Clasts in the Exeter Group, from unroofing of the Dartmoor Granite, first occurred at a minimum of c. 8 myr after formation of the granite.